Method for frequency distortion of an audio signal, method for suppressing an acoustic feedback in an acoustic system and hearing aid

1. A method for the frequency distortion of an audio signal, the method comprising the following steps: splitting the audio signal into a plurality of specified frequency bands and defining band limit frequencies by two respective immediately adjacent frequency bands; initially determining a target frequency based on the audio signal for a limit between two frequency ranges with different distortion of the frequencies, and determining a first frequency band based on the target frequency; determining a frequency band having an upper band limit frequency formed by the band limit frequency lying below the target frequency as the first frequency band; determining a second frequency band lying immediately above the first frequency band based on the audio signal; and applying a distortion of the frequencies differing from the distortion applied to signal components in the second frequency band to signal components in the first frequency band and generating a resulting frequency-distorted signal.

2. The method according to claim 1 , which further comprises determining the frequency band having an upper band limit frequency formed by the band limit frequency lying immediately below the target frequency as the first frequency band.

3. The method according to claim 1 , which further comprises: at a time following the determination of the first frequency band, determining a third frequency band differing from the first frequency band by using the audio signal; and applying a distortion of the frequencies differing from the distortion applied to signal components in a frequency band immediately adjacent the third frequency band to signal components in the third frequency band.

4. The method according to claim 3 , which further comprises initially determining a second target frequency differing from the first target frequency based on the audio signal in order to determine the third frequency band, and determining the third frequency band based on the second target frequency.

5. The method according to claim 4 , which further comprises: performing a check to determine whether the second target frequency lies immediately above an upper band limit frequency of a further frequency band differing from the first frequency band; determining the further frequency band as the third frequency band depending on the check; and applying a distortion of the frequencies differing from the distortion applied to the signal components of the frequency band lying immediately above the third frequency band to the signal components in the third frequency band.

6. The method according to claim 1 , which further comprises providing the distortion of each of the frequencies as a shift by at least one of an amount being constant throughout the frequency or a frequency value modulated in a time-dependent manner.

7. The method according to claim 1 , which further comprises always carrying out a change in the distortion of the frequencies to be applied to the signal component in a frequency band in such a way that a phase of the frequency-distorted signal component does not jump or jumps only to an extent understepping a limit value due to the change.

8. The method according to claim 1 , which further comprises carrying out a change in the distortion of the frequencies to be applied to the signal component in a frequency band only in a zero crossing or in a specified vicinity of a zero crossing of a phase modification of the frequency-distorted signal component correlated with the distortion.

9. The method according to claim 1 , which further comprises additionally filtering at least one of: the first frequency band with a low-pass filter or the second frequency band with a high-pass filter.

10. The method according to claim 9 , which further comprises shifting the band limit frequency between the first frequency band and the second frequency band from a value specified by the splitting of the frequency bands toward the first target frequency by using at least one of a filter characteristic of the low-pass filter or a filter characteristic of the high-pass filter.

11. The method according to claim 1 , which further comprises applying the distortion of frequencies only to signal components of frequency bands on one side of the band limit frequency between the first frequency band and the second frequency band.

12. A method for suppressing an acoustic feedback in an acoustic system, the method comprising the following steps: using an input converter of the acoustic system to generate an input signal from a sound signal of the environment; generating an intermediate signal based on the input signal and feeding the intermediate signal to a signal processing unit with a filter bank for a frequency-band-based splitting of the intermediate signal; generating an output signal from a frequency-distorted signal and converting the output signal into an output sound signal by using an output converter of the acoustic system; suppressing an acoustic feedback occurring due to an injection of the output sound signal into the input converter in the acoustic system based on the frequency-distorted signal; and applying the method for the frequency distortion according to claim 1 to the intermediate signal to generate the frequency-distorted signal.

13. A hearing aid, comprising: an input converter for generating an input signal from a sound signal of the environment; a signal processing unit with a filter bank for splitting an audio signal derived from the input signal based on the input signal; and a control unit configured to carry out the method according to claim 1 .